The antioxidant activity of a set of 17 active principles present in foods is studied by using two sets of methods: i) spectrophotometric, DPPH radical scavenging method and CUPRAC assay; ii) electrochemical, using either a mercury electrode or a glassy carbon electrode covered with poly-neutral red and doped with Pt nanoparticles. The modified glassy carbon electrode assesses the scavenging activity of the antioxidants studied, improving the measurement time and easiness respect to the rest of the methods. Compared to Hg electrode, the measurements can be made in conditions close to the physiological conditions (pH 7 and aqueous medium). Using this sensor, antioxidants without activity in the DPPH radical scavenging assay can be studied. Finally, with respect to CUPRAC, the advantages of the modified electrode are the absence of organic solvent, with the consequent closeness to physiological conditions, and the lower measuring time involved. The sensitivity of this sensor is comparable with those shown by DPPH or CUPRAC.

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Six polyphenazine electrodes modified with platinum and silver nanoparticles deposited over conducting polymers have been prepared using electrochemical techniques. Phenazine monomers were electropolymerized on Indium tin oxide (ITO) and their morphology was explored by SEM-EDX and Raman spectroscopy. The main findings indicated that the polymers are not homogenously electrodeposited, having pores where metal nanoparticles can be nested, which can play an important role in the ionic exchange with the electrolyte. At longer deposition times, formation of clusters is observed with a loss of electrocatalytic activity and at shorter deposition times the growth step is not yet started and catalysis does not occur. Platinum nanoparticles with sizes of 10-60 nm are formed on the polymer agglomerates. Electrochemical measurements of H2O2 and H2O2-ascorbic acid were carried out as a model system and the electrodes have been characterized by SEM-EDX. The size of the nanoparticles and their aggregates decreased with respect to those of the original size. After an electrochemical cleaning, the sizes of aggregates were recovered which justify the reproducibility of the sensor. For Ag/Polymer/ITO, in all of cases, formation of dendrites plus silver nanoparticles was observed by SEM-EDX.